The present invention relates to silver halide photographic sensitive materials and, particularly, to silver halide photographic sensitive materials having an improved covering power which cause a remarkably lower degree of reticulation and can reduce the amount of scum formed in the developing solution.
Generally, in order to shorten developing time of sensitive materials the developing temperature is gradually increased to about 27.degree. C. or more. The shorter developing time can be obtained by using an automatic developing apparatus capable of carrying out rapid development with good reproduction as described in U.S. Pat. Nos. 3,025,779 and 3,672,288, and Rodal Technol. 44 No. 4 257-261 (1973). The automatic developing apparatus generally includes a developing bath, a stopping bath, a fixing bath, a water wash bath and a drying zone. The conveying rate of films and processing temperature can be controlled within the apparatus.
Farnell et al (J. Phot. Sci., vol. 18 page 94 (1970)) discloses that the covering power of photographic sensitive materials using silver halide emulsions can be improved by varying the degree of hardening of the gelatine binder in order to vary the degree of swelling in the processing solution. It has been noted that the covering power increases with a decrease of the degree of hardening of the silver halide sensitive layer by reducing the amount of a hardening agent. However, if the degree of hardening is extremely low, the strength of the emulsion layer deteriorates remarkably. Accordingly, when processed with the above described automatic developing apparatus, the silver halide emulsion layer is easily separated from the base and/or the emulsion layer is easily scratched by handling during the processing. Further, as another problem, the binder which may come out of the sensitive material, alone or by bonding to other components in the processing solution and/or the sensitive material, sometimes forms insoluble sediments in the processing solution in the automatic developing apparatus. Such insoluble sediments in the processing solution are generally referred to as "scum" in this field. When the scum is formed in the processing solution, it adheres to the sensitive material passing through the automatic developing apparatus resulting in a considerable amount of pollution. The scum adhering to the sensitive material causes remarkable deterioration of the quantity of images on the sensitive material, by which the commercial value is lost entirely.
Further, if high temperature rapid treatment is carried out, the photographic sensitive emulsion layer and other layers swell and soften excessively and this causes physical strength to deteriorate and frequently causes the formation of network patterns called reticulation on the surface.
Accordingly, the degree of hardening of the silver halide emulsion layer must be increased to some degree in order to improve the above described problems. However, as the degree of hardening is increased the covering power descreases. Although there are many known methods of hardening the silver halide emulsion layer, none of them overcome the above described contrary relationship.
As a result of studies relating to improving such problems, it is found that the drawbacks caused by scum can be substantially eliminated if the hardness of the insensitive upmost layer (hereinafter, referred to as "upmost layer") is increased utilizing a hardening technique capable of controlling the hardness of the upmost layer and that of the silver halide emulsion layer, separately.
When dealing with multilayer coating materials, if the upmost layer is hardened so as to have a hardness higher than that of the lower layer, network patterns called "reticulation" occur. Accordingly, there is deterioration of the covering power according to the degree of reticulation when carried out a high temperature treatment. (edited by R. J. Cox; Tojos. Photographic Gelatin, pages 49-61, (1972), Academic Press).
A method for preventing the occurrence of reticulation involves adding carboxymethyl casein or sodium ethyl cellulose sulfate to the uppermost layer as described in (U.S. Pat. No. 887,012), or adding a carboxyl group containing polymer as described in (Japanese Patent Application (OPI) No. 36021/77) or adding acid-treated gelatine as described in (Japanese Patent Application (OPI) No. 6017/76). However, these methods are not always suitable, because the polymer dissolves in the processing solution during processing which form scums. Furthermore, there processes have many production problems.